release: v0.4.0

Author: vanyarock01

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+
+## [0.4.0] - 2020-07-14
 ### Added
 - New default metrics: cpu_total, cpu_thread
 - histogram:observe_latency for measure latency of function call with example